Biology · Neural Control and Coordination · NEET
When a neuron is resting (not carrying any impulse), there is a charge difference across its membrane: the outer surface is positive and the inner surface is negative. This electrical potential difference across the resting membrane is called the resting potential. The membrane in this state is called polarised.
At rest, the axonal membrane is comparatively MORE permeable to potassium ions (K+) and nearly impermeable to sodium ions (Na+). It is also impermeable to the negatively charged proteins inside the axoplasm. This selective permeability is a main reason the resting potential exists.
Inside (axoplasm): HIGH K+ and negatively charged proteins, LOW Na+. Outside the axon: LOW K+ and HIGH Na+. This sets up a concentration gradient for each ion across the resting membrane.
The ionic gradients across the resting membrane are maintained by active transport of ions by the sodium-potassium pump. This pump moves 3 Na+ OUT of the cell for every 2 K+ it moves IN. Because it pumps against the gradients, it uses ATP (energy), which is why the setup stays stable at rest.
The Na+/K+ pump pushes out 3 positive Na+ but brings in only 2 positive K+. So more positive charge leaves than enters, leaving the outer surface positive and the inner surface negative. Combined with the trapped negative proteins inside, the inside stays negative.
They describe the same resting state from two angles. Polarised means charge is separated across the membrane (outside +, inside -). Resting potential is the actual voltage (potential difference) that this polarisation produces. So a polarised membrane HAS a resting potential.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the electrical potential difference across the plasma membrane of a resting (non-conducting) neuron, where the outer surface is positively charged and the inner surface is negatively charged.
By the active transport of ions through the sodium-potassium pump, which transports 3 Na+ outwards for every 2 K+ into the cell, maintaining the ionic concentration gradients across the membrane.
Potassium ions (K+) are higher inside the axoplasm, along with negatively charged proteins, while sodium ions (Na+) are higher outside the axon.
Because charges are separated across it: the outer surface carries positive charge and the inner surface carries negative charge. This separation is called polarisation.
Yes. The sodium-potassium pump moves ions against their concentration gradients by active transport, so it uses ATP to keep the gradients and the resting potential stable.
